Evidence of Evolution

1. Evidence of Evolution Molecular Biology, Homologies, and Vestigial Structures

2. Molecular Evidence of Evolution • There is a vast amount of molecular evidence for evolution and common ancestry! We could have spent an entire semester on molecular evidence of evolution and still not have covered everything, but let’s see what we can do in about ten minutes!

3. Molecular Uniformity The Universal Tree of Life

4. Examples of Molecular Uniformity- from the broad to the specific • All living organisms use DNA as their genetic material • All DNA uses the exact same 4 nucleotides  A, T, G, C • The Genetic Code is the same for all organisms  DNA is read 3 letters at a time in order to construct proteins • Each particular sequence of 3 nucleotides act as a pattern for exactly the same amino acid in every living organism. In other words, the codons are uniform  all code for the same amino acid!

5. Examples of Molecular Uniformity- from the broad to the specific • The amino acids used by living things are the exact same. There are hundreds of amino acids and all living things use the exact same twenty amino acids to construct their proteins. • In addition to using the same twenty amino acids, all species use the L- optical Isomer form of the amino acids. This distinction is a little arbitrary… we could use the L or the D isomers, but ALL living things use the L- optical isomers of amino acids. • The metabolic pathways used by living organisms – like respiration – are remarkably similar, even among very distant organisms.

6. Examples of Molecular Uniformity- from the broad to the specific • More closely related organisms are more genetically similar. A branching tree of relatedness can be constructed using similarities in DNA. The more recent the shared ancestry, the more similar the DNA. As you move farther from that common ancestor on the tree, the differences in DNA build up progressively.

7. Examples of Molecular Uniformity- from the broad to the specific • The degree of similarity in the sequence of nucleotides or amino acids can be precisely quantified. For example, Cytochrome C is a protein used in cellular respiration in all living organisms. We can expect to find more molecular difference in this protein with more evolutionary distance. • There are 104 amino acids in Cytochrome C. Our version differs from that of the Rhesus Monkey by 1 amino acid, differs from horses by 12 amino acids, and differs from the Cytochrome C of a Tuna by 33 amino acids. We can use such information to construct evolutionary relationships among organisms.

8. What’s the Significance? • It didn’t have to be this way! • This molecular uniformity and genetic continuity reveals the common ancestry of all organisms. • It is no more necessary for all of these molecular similarities to exist than it would be for all the world’s different languages to represent the idea of “Tree” using the exact same letters to convey the exact same meaning. T-R-E-E conveying the idea of

9. An Illustration… • Let us assume that we are comparing two books • Both are 200 pages and have the same number of chapters • Both are identical, word-for-word, except for the occasional word. Say, 1 out of every 100 words were different.

10. An illustration… • The likelihood that these two books could have been produced independently is infinitesimally small. • Either the books are copied from each other, or both have been copied, either directly or indirectly, from the same original book. • THAT is the significance of the molecular evidence of evolution

11. Other Types of Evidence for Evolution Homologous Structures, Vestigial Structures, and Embryology

12. Homologous Structures • Structures that have different mature forms, but develop from the same embryonic tissues. • For example, the limbs of reptiles, birds, and mammals are hugely different in form and function, yet they are all constructed from the same bones! • These limb bones all develop from the same clump of cells in embryos.

13. Embryology • The early stages of vertebrates (animals with backbones) are very similar and give clues to ancestral relationships. • Gill slits and tails are present in the early stages of human development.

14. Embryology • The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues found in all vertebrates. • These cells, growing in similar ways, are what produce the homologous structures!

15. Vestigial Organs and Structures • A vestigial structure is a structure that no longer performs the function for which it evolved. • It is a remnant of evolutionary history. For example, whales are aquatic mammals that share an ancestry with four legged land animals (it is very closely related to the hippopotamus). It has vestigial pelvic and leg bones “left over” from its evolution.

16. Vestigial Organs and Structures • Sometimes vestigial structures are completely useless and without function (like the whale leg bones), but sometimes the structures are co-opted for other uses (like the wings of an ostrich).

17. Human Vestiges • Appendix • Wisdom Teeth • Sinus Cavities • Coccyx • Muscles for Ear Movement • Goosebumps (Arrector Pili) • PlicaSemilunaris

18. One Final Thing… • Keep in mind that evolution isn’t restricted to physical structures… Behaviors can be adaptations as well. • European Honey Bee VS. Japanese Wasp

19. Adaptations aren’t just for bodies Japanese Honey Bees!!